This invention relates to liquid aircraft runway deicer formulations and more particularly to environmentally friendly deicer formulations that have a minimal effect upon the carbon-carbon fiber composite components in aircraft braking systems and to processes for preparing same. A liquid runaway deicer is defined as composition that is used in conjunction with mechanical means (snow plows, brooms, etc.) to improve the friction of airport pavement surfaces used by aircraft and flight line support equipment during winter operations or other freezing precipitation events.
Effectiveness and performance or a runway deicer are generally measured in several ways. First, it must be able to melt ice, which is a function of freezing point, ice melting, ice penetration and ice undercutting. The freezing point temperature of the composition is measured as it is diluted with water (the lower the freeze point, the better the deicer). The minimum requirement for a liquid runway deicing fluid is that it has a freeze point lower than (xe2x88x92)14.5 degrees C. when diluted 1:1 with water by weight (SAE AMS 1435, section 3.2.4). The ability to melt ice is measured by the amount of brine generated per gram of deicer applied. Other measured characteristics are how well the deicer penetrates an ice layer, and how well it spreads to undercut the ice once it penetrates the ice layer and reaches the pavement surface.
Secondly, compatibility with aircraft materials and components is essential. This is generally measured by compliance with certain standard corrosion tests with established limits for corrosion rate and/or affect (AMS 1435).
Thirdly, the environmental effect of the deicer is an important consideration, as it becomes part of the snow and ice runoff and finds its way into soils, storm water, and/or treatment faculties. This characteristic is measured by considering how quickly it biodegrades, its effect on aquatic life and its persistence in the environment.
Finally, it must be commercially viable for the producer and economically acceptable to the user.
Modern carbon-carbon composite braking systems used on aircraft are susceptible to catalytic oxidation at high operating temperatures after exposure to certain alkali and alkaline earth elements. This oxidation results in accelerated brake wear, and runway deicers containing those elements are a source of exposure for aircraft brakes.
U.S. Pat. No. 4,913,831 and U.S Pat. No. 5,132,035 teach calcium magnesium acetate granular materials which are environmentally acceptable compositions but, in some instances, may not act with the desired deicing speed. U.S. Pat. No. 5,064,551 discloses acetate and formate solutions for use as deicers which include metal corrosion inhibitors in the form of phosphates and nitrates with EDTA as a surfactant. U.S. Pat. Nos. 5,350,533 and 5,435,930 teach liquid deicing and anti-icing compositions which include an alkali metal acetate, such as potassium acetate, in combination with corrosion inhibitors, such as phosphate ion, alkali metal silicate and triazoles. U.S. Pat. No. 5,772,912 discloses anti-icing compositions purported to be environmentally friendly which can take the form of a homogenized foam including monohydric alcohols or polyhydric alcohols and/or ethers thereof as a freezing point depressant, in combination with xanthan, as a thickener, and an optional corrosion inhibitor.
All of these compositions have been found to have advantages but to also have certain disadvantages, and as a result, the search has continued for compositions that would be economical, environmentally friendly and have minimal potential corrosive effect upon aircraft carbon-carbon fiber composite braking systems.
The invention broadly provides pavement deicing and anti-icing compounds, as well as processes for their manufacture, that contain alkali and alkaline earth metal carboxylates and aliphatic alcohols, along with corrosion-inhibiting additives, which are considered to be more compatible with aircraft carbon-carbon composite brake systems than comparable commercially available formulations.
More specifically, the invention provides runway/pavement deicing and anti-icing compounds that contain alkali and alkaline earth metal carboxylates, aliphatic alcohols and corrosion inhibitors that significantly reduce the catalytic oxidation of aircraft carbon-carbon composite brake systems in comparison to comparable commercially available potassium acetate(KAc)-based products, as well as processes for their manufacture.